1. Field of the Invention
The present invention relates to a vertical machining center.
2. Discussion of the Background
Japanese Laid-open Patent Publication No. 2001-170839, Japanese Laid-open Patent Publication No. 2003-340673 and Japanese Laid-open Utility Model Publication No. 05-53835 (Japanese Utility Model Registration No. 2548646) disclose techniques related to machining centers provided with rotary pallet exchangers.
The pallet exchanger recited in Japanese Laid-open Patent Publication No. 2001-170839 includes bearing-equipped pallet holding stands arranged in a circumferential direction, and a drive shaft that rotates pallets. The rotation shaft rotates a pallet that is being rolled over on the bearing to exchange the pallet. That is, the bearing receives the load of the pallet, which includes the load of a workpiece, and this minimizes the rotational driving force of the pallet exchanger. It is noted that a member above the drive shaft is provided with a partition cover to partition the machining space and the workpiece exchange space from one another. During pallet exchange, the partition cover makes a 180-degree reverse rotation together with the drive shaft, ending up with the front and rear surfaces of the partition cover being arranged in inverse.
Japanese Laid-open Patent Application Publication No. 2003-340673 discloses a pallet exchanger of a horizontal machining center in which a table is movable in a Z axis direction. The pallet exchanger includes a rotation unit that includes a rotation shaft and a pair of arms. The rotation shaft is driven by a driving source. The pair of arms is coupled to the rotation shaft and forms point symmetry relative to the rotation shaft. The rotation shaft, that is, the rotational center of the arms, is offset in an X axis direction relative to a center line of the table. In this configuration, a work door located on a side surface of the machine is closer to the table, and the length of the machine in the Z axis direction is shortened.
In Japanese Laid-open Utility Model Application Publication No. 05-53835, a movement operation command switch on an operation panel is operated to: make a cylinder release a positioning pin that is fixing the pallet exchanger to the bed; couple the pallet exchanger to a saddle; and move the saddle to move the pallet exchanger to a withholding position along a track located on the front of the bed. An area of space accessible by the operator is formed in front of the machine, and the operator stays in the space to perform operations including handling the tool mounted on the spindle.